Hydraulic systems are a very widely used source of motive power for various operations. Hydraulic systems are particularly widely used in vehicles, for example goods vehicles, for operating a number of components of the vehicle. For example, hydraulic systems may be used in tipper trucks for tipping the load carrying part for discharging the load.
Such hydraulic systems typically comprise a pump for pressurising a hydraulic fluid, a valve means for controlling the distribution of pressurised hydraulic fluid and a device which can be operated by the pressurised hydraulic fluid, for example a motor or a piston in a cylinder. These components and the associated pipe work for distributing the pressurised hydraulic fluid are generally referred to as the hydraulic circuit or hydraulic system.
It is desirable to know the condition of the hydraulic fluid in the hydraulic circuit. In particular, it is important to know if the hydraulic fluid is in a pressurised or non-pressurised condition.
For example, an operator may need to know if the means which are driven by hydraulic fluid are actuated. A person maintaining the system may need to know if there is pressurised fluid present in any part of the circuit.
It is particularly important in goods vehicles which have components such as movable bodies to be aware of the condition of the movable bodies. As the movable bodies are typically operated by a hydraulic system, the condition of the movable body can be monitored by checking the hydraulic system.
It is known to provide an alarm for a hydraulic system on a vehicle, comprising a pressure switch which is in communication with the hydraulic system so that pressurised hydraulic fluid can act on the pressure switch to give a signal. An alarm is provided for example in the cap of the vehicle, to give an audible or visual indication of the state of the hydraulic system. In these systems, the pressure switch is located in one part of the vehicle and the alarm generator is located in another part of the vehicle. This is a widely used system, as it places an alarm generator at a position where the driver, who will typically be the operator of the hydraulic system, will be when driving the vehicle. However, this type of alarm is time consuming to install.
Accordingly, it is an object of the present invention to provide an alarm for giving an audible alarm which is dependent on the condition of the hydraulic fluid and which is simple to manufacture and install.
The present inventor has realised that an alarm for indicating the condition of a hydraulic system can be provided in which the alarm generator is integral with the pressure detector. In practice, it is found that the alarm can be made loud enough to be audible to the driver even when the driver is in the cab and the alarm generator is located on a different part of the vehicle. It has been found that this arrangement can simplify the manufacture, installation and maintenance of the alarm, as connections between the pressure detector and the alarm generator can be made very short.